The present invention relates to an apparatus and a method for measuring parameters of a sample which is translucent at least in part.
Translucent products such as for example glass, transparent sheets and the like are used in many fields. In this case the optical properties play an important role, depending upon the field of application. In this way for example, a high degree of transmission is required of glass panels and sheets which are used for greenhouses. A sheet used for packaging, on the other hand, should allow the contents to be recognized as clearly as possible and with as little clouding as possible.
A merely subjective observation of the optical quality of the material, as is nowadays frequently undertaken both in development and, in particular, in production, has the major drawback that the observations cannot be quantified at all or can be quantified only with a rough gradation, so that a comparison of the results is possible to only a very limited degree.
Apparatus have therefore been used in research and development in order to measure for example the degree of transmission of transparent materials. These apparatus have the drawback, however, that they are very complicated and do not allow different optical parameters to be determined which are necessary in order to evaluate the optical quality of the products.
DE 295 11 344 U1 describes an apparatus of this type for measuring optical parameters of transparent materials. In this case an illumination device is provided which irradiates light onto the material to be investigated, as well as a sample-recording space provided after this sample and a plurality of detector devices which detect the light reflected into this space. This apparatus thus allows parameters to be determined in accordance with a specified standard, namely the so-called ASTM standard. This standard is a standard testing method of determining the transmission of transparent plastics materials (ASTM=American Society for Testing Materials). The subject matter of DE 295 11 344 U1 is hereby also made the subject matter of the present application by reference in its entirety.
As well as this standard method, however, there is also a further standard method according to the ISO. In the case of this standard method the intention is also to take into consideration errors which occur as a result of change in efficiency—caused by the samples—of the Ulbricht sphere (integrating sphere) used. In this case for example single-beam methods are used, in which the sample to be investigated is applied to two different outlets of the Ulbricht sphere. In addition, double-beam methods are known, in which two light bundles are used, one constituting the measurement bundle which passes through the sample, and a further bundle which does not pass through the sample but illuminates the inner wall of the Ulbricht sphere. The last-named method has the drawback, however, that the aforesaid light bundles should be precisely attuned to each other and, in addition, influences from the background illumination (for example illumination of the space) should also be taken into consideration.
The object of the present invention is therefore to provide an apparatus and a method which are capable of being used as desired for the two standards named.